To those people who say "free will" exists, what do you even mean by that? What do you think this "free will" is? From what is the will "free"?
Does it mean the will is free from God? But if there were an omniscient & omnipotent God that directly or indirectly created the wills in the first place, then God already knows absolutely everything that is going to happen before, during, and after creation, meaning that the wills are entirely dependent on what God initially caused with absolute knowledge one way or the other.
Does it mean the will is entirely free from the environment? That cannot be it, humans obviously are influenced by what they perceive - otherwise they couldn't react to anything.
Does it mean that reality is not deterministic? That would just imply that reality is probabilistic instead, which would just add fundamental randomness to everything, so a will still isn't actually free from the environment and it's own (past) internal state.
Does it mean the will is free to some definitely limited extent from the environment? That would make sense, insofar that a will can be said to have its own internal state, but then "free will" doesn't mean all that much.
Based on the above, an omniscient & omnipotent God cannot create anything that decides truly independently from that God.
This means this God would be responsible for absolutely all evil from start to finish.
This in turn means the God must itself be the greatest original evil (if it would exist).
The only way to avoid the above is to either:
Claim that the God is not actually omniscient or omnipotent. In that case, what exactly are the limits of that God and why should that be so? Also, why should anyone unconditionally worship that for some reason limited God?
Claim that the God is beyond our reasoning. That would acknowledge that the believe in the God is simply irrational. In that case no rational debate is possible, and any equally irrational believe can use the same non-argument, so why bother talking.
Finally, to those who argue that reality as we know it must have a creator God, what created God then?
If you say God doesn't require a creator, then neither does reality.
If you say reality does require a creator, so does your creator itself.
Adding a creator on top of reality only adds complexity, it doesn't answer anything.
The most straightforward answer to why something exists is that the very absence of anything "before" anything existed, including the very "rules" that define reality, does in fact permit the truly arbitrary "collapse" (for the lack of a better word) into reality. It's not that hard to understand and doesn't require any creator that is more complicated than reality itself.
And even if someone were to still claim that a creator God must exist, this wouldn't alter the prior arguments that this God must be either evil and/or limited in power.